The present invention relates to a disk array system having a plurality of disk drives with a RAID (Redundant Arrays of Independent Disks) configuration, and a method for controlling the disk array system.
In a disk system array system having a plurality of disk drives with a RAID configuration, data processing is performed by driving a plurality of disk drives in parallel. For example, a disk array system, upon receipt of a write command from a host system, adds redundant data to the write data, and then divides the write data among a plurality of disk drives to write the data thereto. Meanwhile, a disk array system, upon receipt of a read command from a host system, reads in parallel the data written among the disk drives, and transmits it to the host system. This kind of disk array system has the function of, upon the occurrence of any failure in any of its disk drives storing data therein, correcting the error using the redundant data, and operating in degraded mode.
In degraded operation, in which redundancy is low, it has been normal to recover data by performing correction copy of the data to a spare disk. When the data recovery to the spare disk is complete and the failed disk drive manually replaced with a new disk drive, the data re-built in the spare disk is copied back to that new disk drive.